This invention relates to a synthetic resin retainer for ball bearings suitable for high-speed rotation and an angular ball bearing.
As an angular ball bearing suitable for high-speed rotation for rotatably supporting a rotary shaft rotated at a high speed, such as a spindle of a machine tool, one described in Japan patent publication 7-4439 is known.
FIG. 15 shows the conventional angular ball bearing. It has a retainer 52 made of a synthetic resin and mounted between an outer ring 50 and an inner ring 51. A ball 54 is accommodated in each of a plurality of pockets 53 formed in the retainer 52 at equal circumferential intervals to support the outer ring 50 and the inner ring 51 so as to be rotatable relative to each other.
The pockets 53 formed in the retainer 52 are cylindrical and are each formed with a conical guide surface 56 at the radially inner end of the cylindrical inner surface 55 so as to be guided by the ball 54. A circumferential, axial and diametric guide clearance 57 is formed between the conical guide surface 56 and the ball 54. The guide clearance 57 is smaller than a pocket clearance 58 formed between the ball 54 and the cylindrical inner surface 55 of each pocket 53.
Here, the radius of curvature r11 of the conical guide surfaces 56 at their radially outer end is equal to the radius of curvature of the cylindrical inner surfaces 55.
In the ball bearing having such a structure, during rotation of the bearing, the balls 54 make point contact with the conical guide surfaces 56, so that a lubricant can flow around the contact points. Thus shortage of a lubricant is less likely to occur.
Further, since the retainer 52 is guided by the balls, the outer and inner peripheral surfaces of the retainer 52 rotate in a non-contact state relative to the outer ring 50 and the inner ring 51, so that no friction noise is produced.
Since the conventional angular ball bearing shown in FIG. 15 is of such a structure that the retainer 52 is supported by contact between the conical guide surfaces 56 and the balls 54, it has the following problem.
That is, when the angular ball bearing rotates at high speed, the balls 54, which rotate about their own axes and about a common axis, contact the conical guide surfaces 56 at point B1 as shown in FIGS. 16 and 17. At this time, each ball 54 rotates about its own axis b shown in FIG. 15. Due to contact with the ball 54, the retainer 52 will axially move, so that the contact point B1 with the ball 54 tends to move toward point B2. But since the distance between point B2 and its opposed point B2′ is shorter than the distance between point B1 and its opposed point B1, the contact point also moves toward the large diameter end of the conical guide surface 56 while moving axially of the retainer 52, and thus moves to the point B3.
Thus, while the angular ball bearing is rotating at high speed, the contact points between the balls 52 and the conical guide surfaces 56 move from point B1 to point B3, so that diametric thrust force is induced in the retainer 52, causing runout of the retainer 52.
Such runout of the retainer 52 is remarkable if used in a vertical position in which the central axis of the angular ball bearing is vertical.
Further, in the conventional angular ball bearing, since a radially outer lubricant filling space 59 formed between the outer ring 50 and the retainer 52 and a radially inner lubricant filling space 60 formed between the retainer 52 and the inner ring 51 communicate with each other through the small pocket clearances 58 and the guide clearances 57, fluidity of the lubricant is so bad that heat tends to build up due to stirring of the lubricant.
Further, since the contact between the balls 54 and the conical guide surfaces 56 is contact between curved surfaces of the balls 54 and the conical guide surfaces 56 having little difference in the radius of curvature, shearing force when lubricant is sheared due to contact with the balls 54 which are rotating about their own axes is large, so that the bearing torque is large.
An object of this invention is to provide a synthetic resin retainer and an angular ball bearing which are less likely to run out during high-speed rotation, can reduce the bearing torque, and are suitable for high-speed rotation.